This invention relates to systems for measurement and indication of vehicular tire air pressure and more particularly for measurement of tire pressure in a moving vehicle.
The importance of maintaining proper air pressure in pneumatic tires for both safety and financial reasons has long been recognized. Tire pressure can be checked manually when a vehicle is stopped, but on some vehicles, such as multi-axle transport trucks, manual checking can be quite time consuming. Many tire failures begin while a vehicle is in motion and it is important for the driver to know of a slow loss of pressure before the tire becomes dangerously deflated. Many tire pressure warning systems have been devised and patented, but most only warn of loss of pressure below a fixed threshold or require complex and unreliable commutating elements to be built into an axle. Some threshold sensing devices such as that disclosed in U.S. Pat. No. 2,710,391 issued to F. Trinca on June 7, 1955, have a mechanical finger which extends from a wheel mounted sensor upon a loss of pressure to move the arm of a chassis mounted switch on each tire revolution. Other threshold sensing devices, such as that disclosed in U.S. Pat. No. 3,638,180 issued to Daniel Lejeune on Jan. 25, 1972, have a magnet which moves upon a loss of pressure to cause a reed switch to close each time the sensor passes. In some warning systems such as that disclosed in U.S. Pat. No. 3,162,835 issued to W. H. Dudar on Dec. 22, 1964, a wheel mounted pressure sensor is coupled to a chassis mounted annunciator by means of a slip ring built into an axle. Still other sensing systems, such as that disclosed in U.S. Pat. No. 3,215,978, issued to H. M. Brown et al on Nov. 2, 1965 include a radio frequency transmitter mounted on each wheel in addition to a pressure sensing switch which activates the transmitter upon a loss of tire pressure. In this system a chassis mounted receiver detects the signal and generates a warning for the driver. The systems characterized by slip ring contacts or radio transmitters could be modified to include actual pressure measuring sensors, but at the cost of increased complexity of the wheel sensor and the requirement that power must be supplied to the wheel mounted sensor. The above referenced Brown patent discloses a battery powered transmitter, but it only operates when a failure occurs, and more power would be required for continuous operation. All the other systems are limited to pressure threshold sensing and not actual pressure measuring.